Ventrociliella romanae Kolasa, 1977

Houben, Albrecht M., Monnens, Marlies, Proesmans, Willem & Artois, Tom J., 2022, Limnoterrestrial ‘ Typhloplanidae’ (Rhabdocoela, Platyhelminthes), with the description of four new species and a new genus, European Journal of Taxonomy 798, pp. 70-102 : 77-79

Ventrociliella romanae Kolasa, 1977

Fig. 3

Material examined

AUSTRIA • 1 spec., serially sectioned; near Graz, Hohe Rannach ; 47°09′53″ N, 15°24′50″ E; 26 Aug. 2011; A.M. Houben and W. Proesmans leg.; leafy humus of a birch forest; XIV.2.34; HU • 1 spec., live observations; Graz, Rohrenberg ; 47°07′44″ N, 15°24′53″ E; 26 Aug. 2011; A.M. Houben and W. Proesmans leg.; between dead leaves • 2 specs, serially sectioned; Graz, Kanzelkügel ; 47°06′49″ N, 15°23′11″ E; 26 Aug. 2011; leafy humus; XIV.2.35–XIV.2.36; HU • 1 spec., live observations; Weyer, Kreuzberg ; 47°51′36″ N, 14°39′09″ E; 26 Aug. 2011; A.M. Houben and W. Proesmans leg.; humus of a mixed forest • 4 specs, live observations, one of which serially sectioned; Weyer, Kreuzberg ; 47°51′29″ N, 14°39′14″ E; 26 Aug. 2011; A.M. Houben and W. Proesmans leg.; moss growing on a dead trunk; XIV.2.37; HU.

Description and discussion

The specimens from Austria are about 0.8mm long and very dark due to their gut content ( Fig. 3B ). Habitus and internal organs are as described by Kolasa (1977), with the exception that protonephridiopores of one specimen (not drawn) are situated just anterior to the pharynx and not lateral to or slightly behind the pharynx as originally described. However, in most specimens, they are situated at ±50% of the body (pp,

Fig. 3A ). Due to the small size of the specimens, it was not possible to make a thorough reconstruction of the reproductive structures from the sectioned specimens.

Although Ventrociliella romanae was originally placed within ’Protoplanellinae’, it was recently listed as a taxon incertae sedis within Dalytyphloplanida ( Van Steenkiste et al. 2010). Awaiting the inclusion of this taxon in molecular phylogenetic analyses, we for now keep this genus as incertae sedis, with probably a high affiliation to ‘Protoplanellinae’: Kolasa (1977) considered V. romanae closely related to the protoplanellin Bockia deses Reisinger, 1924 because of their similar habitus, the position of the male reproductive organ, the construction of the pharynx, and their limnoterrestrial lifestyle. Indeed, the only drawing ever published of B. deses ( Reisinger 1954: fig. 10) closely resembles the drawing we constructed of a free-swimming specimen of V. romanae ( Fig. 3B ). Considering their similarity, and especially since the description of B. deses is based on a single specimen, a re-assessment of the validity of these species is warranted. As we found new material of V. romanae on the type locality of B. deses, we here present a detailed morphological comparison between both species.

Kolasa (1977) stated that V. romanae and B. deses differ due to the presence of (1) a real pharynx doliiformis, (2) the lack of adenal rhabdites, (3) the absence of a bursa, (4) the occurrence of ciliation all over the body, (5) the lack of a seminal receptacle, and (6) a sclerotised ejaculatory duct. However, the pharynx of V. romanae is strongly tilted forwards, which makes it possible to describe it as a pharynx doliiformis (1). Furthermore, in some of our specimens of V. romanae, adenal rhabdites are barely visible and may easily be overlooked (2). The bursa originally described by Kolasa (1977) was sometimes seen as a large genital atrium, a characteristic also mentioned in the description of B. deses ( Reisinger 1924) (3). Reisinger (1924) never made any remarks on body ciliation. Indeed, this is a rather subtle characteristic and may have easily been missed on a single specimen (4). As the seminal vesicle of V. romanae is merely an accumulation of sperm in the oviduct, it could be easily overlooked if it is not filled. Therefore, the absence of this vesicle in B. deses has little diagnostic value (5). The only clear difference between the two species may be that the ejaculatory duct of B. deses is slightly sclerotised, while it is muscular in V. romanae. However, considering their small size and the absence of sectioned material of B. deses, the reliability of this characteristic is also questionable (6). Finally, the typical, conspicuous, vacuolated epidermis of V. romanae was never mentioned for B. deses.

As all presumed differences are questionable to some degree, it is highly likely that V. romanae and B. deses belong to the same genus or perhaps are synonyms. In the latter case, V. romanae would become the junior synonym of B. deses. Resolving this possible synonymy is a challenging task, as specimens identified as either species are reported from the same (type) locality. A more exhaustive resampling effort on this sampling locality may provide more clarity: Microscopical study of a large sample may or may not reveal a consistent difference in the above-mentioned morphological traits, possibly demonstrating their diagnostic value. Sequencing morphologically vouchered representatives of both presumed species and subsequent molecular delineation methods may then provide further evidence for the validity of these taxa. However, with the data available today, Bockia deses is better considered a nomen dubium.

Previously known distribution

Forest soil near the stream Fosso Contesora in Tuscany, Italy ( Kolasa 1977).

Figures

Fig. 3. Ventrociliella romanae Kolasa, 1977. A. Internal organisation of a live specimen. B. Habitus of a live specimen.